re than threefold the great
original domain of the United States had been made by honorable purchase
or less honorable conquest. It had not added largely to the population
of the nation; the new acquisitions were mainly of unoccupied land. The
increase of the population, down to about 1845, was chiefly the natural
increase of a hardy and prolific stock under conditions in the highest
degree favorable to such increase. Up to the year 1820 the recent
immigration had been inconsiderable. In the ten years 1820-29 the annual
arrival of immigrants was nine thousand. In the next decade, 1830-39,
the annual arrival was nearly thirty-five thousand, or a hundred a day.
For forty years the total immigration from all quarters was much less
than a half-million. In the course of the next three decades, from 1840
to 1869, there arrived in the United States from the various countries
of Europe five and a half millions of people. It was more than the
entire population of the country at the time of the first census;--

A multitude like which the populous North
Poured never from her frozen loins to pass
Rhene or the Danaw, when her barbarous sons
Came like a deluge on the South and spread
Beneath Gibraltar to the Libyan sands.

Under the pressure of a less copious flood of incursion the greatest
empire in all history, strongest in arts and polity as well as arms, had
perished utterly. If Rome, with her population of one hundred and twenty
millions, her genius for war and government, and her long-compacted
civilization, succumbed under a less sudden rush of invasion, what hope
was there for the young American Republic, with its scanty population
and its new and untried institutions?[316:1]

An impressive providential combination of causes determined this great
historic movement of population at this time. It was effected by
attractions in front of the emigrant, reinforced by impulses from
behind. The conclusion of the peace of 1815 was followed by the
beginning of an era of great public works, one of the first of which was
the digging of the Erie Canal. This sort of enterprise makes an
immediate demand for large forces of unskilled laborers; and in both
hemispheres it has been observed to occasion movements of population out
of Catholic countries into Protestant countries. The westward current
of the indigenous population created a vacuum in the seaboard States,
and a demand for labor that was soon felt in the l